The invention relates to the telecommunications field and, more particularly, to a process for transporting a cell through a switching structure which is based on a single stage switch.
Patent applications EP 96480126.0 (IBM Docket FR996040), EP 96480125.2 (IBM Docket FR996041), EP 96480117.9 (IBM Docket FR996042), and EP 96480120.3 (IBM Docket FR996045) are nonpublished prior European applications representing examples of powerful self-routing switches that provide high switching speed.
Powerful telecommunications switches operating at speeds greater than hundreds of Gigabits per second are now developed. The data which are to be switched by these elements are generally provided from telecommunications links, such as X25, which are generally located at a distance greater than a hundred meters from the switching structure. Such distances are attributable to the fact that the different telecommunications links are located in different parts within an industrial area, e.g. a manufacturing site of a company.
Additionally, the data which is to be switched today takes the form of data cells, generally of a given length, which may of course comply with the well-known Asynchronous Transfer Mode (ATM) format. This cell generally comprises, in addition to the payload containing the useful data to be transported, a routing header that is used for determining the direction to be taken within the switching structure. However the generally small size of the cell prohibits the header from having a large size, jeopardizing the efficiency of the switch. This theoretically limits the possibilities of the routing processing, and particularly the multicasting possibility.
In addition, since the different points of entry and output of the switch are located at different locations, that may be separated by a distance of greater than one hundred meters, the data cells have to be serialized at a given location in order to permit this transport within the area of the industrial site, which also results in difficulties for providing cell synchronization.
Furthermore, the data cells have to be converted to a form that is particularly adapted to the structure of the switching element, i. e., the switch core, which will route the cells to the appropriate direction.
The problem to be solved by the invention is to provide a process for transporting a data cell, entered at a remote point within an industrial premises, throughout a switching structure which is based on a single stage switch, and to route the cell towards the appropriate direction to a point that is located in a second remote area. Since the size of the cell is small and the power of the switch is high, the process must not jeopardize the efficiency of the switching structure. A number of formatting steps on the cells is included for permitting an appropriate manipulation of the data cell at the different levels of the switching structure, particularly including serialization/deserialization, the routing process and the correction for the difference in the transport times within the local switching structure.
This problem is solved by the present invention as defined in claim 1. Basically the process comprises a number of formatting steps that allow the data cell to be structured and that presents a form permitting an efficient transport throughout the entire switching structure, i.e., the switch fabric. Thus, the cell automatically passes through the different elements of the switching structure and is routed to the appropriate elements.
Remotely with respect to the switch core (i.e., the switching part of the switch fabric that is generally located in one building of the industrial site), the data cell which is received from a telecommunications link is formatted in order to permit the transport through k serialized link lines to the local switching structure. This formatting includes dividing the cell in k logical units (LUs) and adding routing bytes, that is to say extra bytes that are specially reserved for preparing the routing process throughout the switching structure. In addition, the k logical units are coded by means of the 8B/10B coding process in order to permit the cell clock transport within each serialized link. In order to preserve the bandwidth, the coding is such that a comma character is introduced in each empty cell so that the size of the useful data cell is not affected.
Locally, within the switch core, the k coded LUs which enter the local switching structure are then deserialized and the cell clock is obtained for each cell in order to reconstitute the data cell. In addition, at this point, reservations for the routing bytes are filled with their appropriate values (bit map) that will be used for the routing process within the switch by means of an access to an entry routing table.
In the case where the switch core is based on m switching elements operating in parallel (speed expansion mode), the data cell is divided into m separate data fields which can be entered within the m parallel switching elements. The bit map is used for controlling the routing process.
Locally, when the cell outputs the switching structure, a second access to a routing table permits the replacement of the previous bit map by new values in order to enhance multicast capabilities.
The data cell is then divided again in a set of k serialized Logical Units (LUs) in order to prepare a serialization through k links. The LUs are then coded by means of the 8B/10B coding process and comma characters are introduced again. The comma characters which are introduced can be used for providing LU merging process when different sets of switches operated in parallel are connected in a port expansion mode.
Remotely with respect to the switch core, the coded LUs are deserialized and the data cell is reconstituted by means of the deserialization and permitted by the reconstitution of the data cell clock transported by the 8B/10B coding process. The newly inserted values of the bit map are then used for enhancing multicasting capabilities.
The reservations for routing bytes can then be suppressed before the cell is provided to the telecommunications link by means of an appropriate Protocol Engine.
It appears that, from a remotely located entry point in a switching structure and up to a second remotely located point and passing through the local switch core, there is provided a packing process of the cell which gives it the appropriate form at every level within the switch fabric so that it can very quickly be routed towards the appropriate direction port.
The reservations for routing bytes which is introduced at the entry point of the switch fabric and suppressed before it is outputted from the switch fabric, and which at two different levels is replaced by appropriate routing values, permits the cell to keep a maximum size for transporting useful data and for preserving the bandwidth. The use of comma characters inside empty cells enhances this advantage, and further, provides the possibility to synchronize the cells (in the form of LUs), that come from different switching structures connected in port expansion mode.
These advantages are provided by means of the very efficient cooperation of the routing bit reservation, which can be replaced at different steps by the appropriate bit map value, with the 8B/10B bit coding process and the introduction of the comma characters inside the empty cells which are used as well as for LU synchronization and different in transport times within the local switch cores. A very efficient packing method for the data cell is provided so that the data cell can be transported and processed throughout the switch fabric structure, the overall processing comprising serialization/deserialization, routing and multicasting, and time compensation in the transport of the cell in the local switch core when operating in port expansion mode.